1. Field of the Invention
The present invention relates to a method for preparing a cellulose solution, which can be made into various products such as filaments, fibers, films, membranes, etc., by means of using a new organic solvent system.
2. Description of the Prior Art
Various studies and experiments have in recent years been made aiming to prepare some cellulose solutions, which may produce various articles having desired shapes, by dissolving cellulose in an organic solvent. Principal objects of those studies and experiments can be summarized into two groups: (1) A first of them is conceived to provide a new production equipment original or unique enough to replace the traditional viscose method, in respect to reducing the investment cost and decreasing the controversial environment contamination. This object is to be attained by collecting and uniting the production processes into a simple style. (2) And a second group is conceived to provide various new cellulose products having excellent features, without chemically changing or denaturing the cellulose itself and decreasing or degrading so much the degree of polymerization thereof. This object can be achieved by making the cellulose dissolve in an organic solvent at a high degree of concentration.
The inventors who had carefully studied most of known representative methods for dissolving cellulose came however to a conclusion that each of them can not be free from some shortcomings, while being advantageous in some respects. Some methods are still defective, because the then used solvent itself constitutes an environment-contaminating matter; some are too expensive for being carried into practical use; some are difficult in the handling of the solvent or in the recovery of the same; in some other methods the cellulose itself cannot escape from being affected by a chemical change and thereby greatly sacrificing the desired high degree of polymerization thereof.
Further, according to the following reports: (1) a patent specification of U.S. Pat. No. 1,943,176; and (2) an article entitled "N-Athyl-pyridinium-chlorid als Losungsmittel und Reaktionsmedium fur Cellulose", Von E. Huseman und E. Siefelt, [Die Makromolekulare Chemie, 128 (1969) Seite 288-291], cellulose is dissolved with N-ethyl pyridinium chloride, which can be obtained by treating pyridine with ethyl chloride, either applied alone or in combination with any solvent. The above introduced traditional method is referred to as EPy.Cl process for short. This very EPy.Cl process is also intrinsically involved in the aforementioned problems a great deal, and thereby far from being satisfactory as a practical manufacturing process of a cellulose solution.